Optical fiber connectors are a critical part of essentially all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices, such as radiation sources, detectors and repeaters, and to connect fiber to passive devices, such as switches, multiplexers, and attenuators. The principal function of an optical fiber connector is to hold the fiber end such that the fiber's core is axially aligned with an optical pathway of the mating structure. This way, light from the fiber is optically coupled to the optical pathway.
Of particular interest herein are “expanded beam” optical connectors. Such connectors are used traditionally in high vibration and/or dirty environments, where “physical contact” between the fiber and the light path of mating connector is problematic. Specifically, in dirty environments, particulates may become trapped between connectors during mating. Such debris has a profoundly detrimental effect on the optical transmission since the particles are relatively large compared to the optical path (e.g., 10 microns diameter in single mode) and are therefore likely to block at least a portion of the optical transmission. Furthermore, in high-vibration environments, optical connectors having ferrules in physical contact tend to experience scratching at their interface. This scratching diminishes the finish of the fiber end face, thereby increasing reflective loss and scattering.
To avoid problems of debris and vibration, a connector has been developed which expands the optical beam and transmits it over an air gap between the connectors. By expanding the beam, its relative size increases with respect to the debris, making it less susceptible to interference. Further, transmitting the beam over an air gap eliminates component-to-component wear, thereby increasing the connector's endurance to vibration. Over the years, the expanded beam connector has evolved into a ruggedized multi-fiber connector comprising an outer housing which is configured to mate with the outer housing of a mating connector, typically through a screw connection. Contained within the outer housing are a number of inner assemblies or “inserts.” Each insert comprises an insert housing, a ferrule assembly contained within the insert housing and adapted to receive a fiber, and a ball lens at a mating end of the insert housing optically connected to the fiber. The ball lens serves to expand and collimate light through (or near) the connector interface. When two expanded beam connectors are mated, there is an air gap between the ball lenses of each pair of optically coupled inserts.
One of the most demanding tasks for an expanded bean connector is to maintain the optical alignment between the fiber and the lens. Radial offsets of only a few microns can affect insertion losses significantly. The insert assemblies mentioned above have traditionally performed well in maintaining optical alignment in a given channel using alignment pins and a spring force to maintain contact between the insert interfaces.
In U.S. Pat. No. 7,775,725 (herein the “'725 patent,” incorporated by reference in its entirety), a single-channel expanded beam connector is disclosed that exploits the outside dimensions of various optical components to hold and align them in a discrete optical subassembly. These components can then be held in alignment in a compact, cylindrical sleeve to form the subassembly. This patent also discloses optically coupling different optical devices by conveniently aligning the subassembly of each device in a second, common sleeve. Thus, the patent discloses a single-channel connector having a small form factor and a low insertion loss (good optical alignment).
Although the '725 patent discloses a compact and reliable alignment approach for expanded beam connectors, Applicant has identified the need for a field installable expanded-beam connector system. The preset invention fulfills this need among others.